[Halld-pid] TOF PMT gain and rates

[Paul Eugenio]

Hi Beni,

Recall originally the plan was to use XP2020UR tubes.  The XP2020UR is a 12 stage tube with gains of 5E7.  The Hamamatsu R10533 which had an average gain of 1E6 (now 4E6) is the 10 stage version of their ultra-fast 8-stage R9779 tube.   

We did comparative test between the R105343 and the XP2020UR.  The timing, based on time difference were comparable.  We even showed that the  R105343 show slightly better resolution.    

Since the gain of  R105343 was 1.5 orders of magnitude less that the XP2020's,  we measured the counter efficiency as a function of hit location along the scintillator (0 - 100 inches).   The efficiencies of the XP2020 tubes were fine, but we found that one of the  R105343 tubes (the lower gain tube) was less efficient(97% for hits 95" away) at detecting the hits which emanated at the opposite end of the scintillator.  At the time, we had two  R105343 tubes, one with gain 1.1E6 and the other with gain 1.5E6.    These tubes were one the first of this type made by Hamamatsu.  Also at the time, they promised an average gain of 2E6 with 1E6 minimum.  Now, their average gains are 4.2E6 of which we have a requirement that the minimum gain for selection be 2E6.    This is the so called "FSU push for high gain PMTs".     

The average anode current for the R105343 listed on the spec sheet is 0.1 mA.  You say that we can not operate the PMT at a gain that results in currents that the close to 0.1mA.   Are you sure that you are not off by a factor of ten?




--
Prof. Paul Eugenio
Florida State University
Department of Physics
Tallahassee, Florida,  USA 32306

(850) 325-0314
eugenio at fsu.edu




On Sep 19, 2011, at 9:11 AM, Beni Zihlmann wrote:

> Hi All,
> last Friday the Hamamatsu representatives were here at the lab and
> we had a short conversation about the TOF PMTs. From this short
> meeting I conclude that we need an extensive discussion about the
> PMTs.
> One important issue is that here at Jlab we do not understand why
> you at FSU push so hard for high gain PMTs. Even at the low intensity
> beam of 10^7 photons the inner most paddles will see rates of about
> 1 MHz and consequently the current in the PMT will be substantial if
> the gain is high. We can not operate the PMT at a gain that results in
> currents that the close to 0.1mA. Such currents will diminish the intrinsic
> gain of the PMT substantially in a short time (50% in 1000 hours operation).
> 
> Can you estimate how many photo electrons you get for a MIP that passes
> through the center of the paddle and deposits the mean energy of a landau
> distribution? Having signals of 1000mV for such events will results in too
> high currents.
> 
> I would like to put this issue on the agenda for next meeting.
> 
> cheers,
> Beni
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